The techniques of atomic force microscopy (“AFM”) and scanning tunneling microscopy (“STM”) are used to create three-dimensional topographic maps of a surface, providing a level of detail that approaches, the case of STM, atomic resolution. These methods generally rely upon the use of a sharp tip to sense the topography of a surface, including the position of particles and objects on that surface, with tunneling current or force data being used to provide the topographic information. These tips are often etched from silicon. See, for example, U.S. Pat. No. 5,242,541, issued Sep. 7, 1993 to Bayer et al. for METHOD OF PRODUCING ULTRAFINE SILICON TIPS FOR THE AFM/STM PROFILOMETRY.
It has also been recognized that nanofibers, such as carbon nanotubes, can make excellent tips for these imaging techniques. See, for example, Dai et al., “NANOTUBES AS NANOPROBES IN SCANNING PROBE MICROSCOPY”, Nature, Vol. 384, 14 Nov. 1° 96, Pages 147-150. One reason for the interest in forming sensing tips out of carbon nanotubes is the high stiffness and aspect ratio common to carbon nanotubes. By way of example, the elastic moduli for carbon nanotubes are similar to those for diamond, as calculated and measured by various researchers, including Sinnott et al., “MECHANICAL PROPERTIES OF NANOTUBE FIBERS AND COMPOSITES DETERMINED FOM THEORETICAL CALCULATIONS AND SIMULATIONS”, Carbon, Vol. 36, Nos. 1-2, Pages 1-9, 1998; and Krishnan et al., “YOUNG'S MODULUS OF SINGLE-WALLED NANOTUBES”, Physical Review B, Vol. 58, No. 20, 15 Nov. 1998, Pages 14013-14019. Furthermore, in U.S. Pat. No. 5,824,470, issued Oct. 20, 1998 to Baldeschwieler et al. for METHOD OF PREPARING PROBES FOR SENSING AND MANIPULATING MICROSCOPIC ENVIRONMENTS AND STRUCTURES, there is taught the chemical modification of a silicon AFM tip to prepare a functionalized tip, which can include a nanotube.
The aforementioned sensing tips are primarily designed to function as interrogation tools, and are generally poorly suited to physically manipulate objects. With the aforementioned sensing tips, object manipulation is generally limited to either pressing an object against a surface or pushing the object across a surface. The aforementioned sensing tips generally lack the ability to pick up, translate or deposit an object elsewhere. If these tips could perform such grasping, translating and deposition functions, a large variety of different patterns, structures, circuits and devices could be assembled with microscale, nanoscale or near atomic resolution.
To perform these more sophisticated manipulation functions, a grasping tool is generally required. In this respect a two element, tweezer-type grasping tool is described in Kim et al., “NANOTUBE NANOTWEEZERS”, Science, Dec. 10, 1999, v286, i5447, p2198. More particularly, Kim et al. teach the construction of a two element tweezer using two nanotubes. One end of each nanotube is adhesively bonded to an electroded micropipette, with the other end of each nanotube remaining free. A pre-determined DC voltage differential selectively applied to the two elements causes electrostatic attraction of the two free tips, thereby causing them to close down on an object.
However, the two element tweezer of Kim et al. can be somewhat unstable and difficult to control, can be relatively difficult to construct, and provides minimal operating control.
More particularly, the two elements of the Kim et al. tweezer together define only a line contact, which is inherently unstable and difficult to control, particularly in a nanoscale device.
In addition, the Kim et al. tweezer is constructed by selectively adhering individual nanotubes to electroded micropipettes. This is, at best, a difficult and inexact procedure, and makes tweezer fabrication problematic inasmuch as alignment, nanotube length and the point of attachment cannot be directly controlled.
Furthermore, Kim et al. used a simple, pre-determined DC voltage to create the attractive and repulsive forces used to close and open the tweezers. This provides minimal operating control.